Method and means for testing magnetic properties of toroid cores



Jan. 24, 1961 R A cMlLLAN 2,969,501

METHOD AND 0R TESTING MAGNETIC PROPERTIES OF TOROID CORES Original FiledAug. 2. 1956 2 Sheets-Sheet 1 Jan. 24, 1961 R. A. M MILLAN 2,969,501

METHOD AND MEANS FOR TESTING MAGNETIC PROPERTIES OF TOROID CORESOriginal Filed Aug. 2. 1956 2 Sheets-Sheet 2 TOR.

INVEN ArMaMJ/Z /7 cM/LLA/v LM A? W 72? -4 gram United States Patent2,969,501 METHOD AND MEANS FOR TESTING MAGNETIC PROPERTIES OF TOROIDCORES Raymond A. MacMillan, Greenwood, Mass., ass'ignor to the UnitedStates of America as represented by the Secretary of the Air ForceOriginal application Aug. 2, 1956, Set. No. 601,351. and thisapplication Sept. 12, 1957, Ser. No.

Claims. 61. s24-- -34) (Granted under Title 35, US. Code (1952), sec.266) The invention described herein may be manufactured and used by orfor the United States Government for governmental purposes withoutpayment to me of any royalty thereon.

This invention relates to the testing of magnetic materials, andparticularly to methods and means for testing toroidal-shaped samples ofsuch magnetic materials.

In order to take measurements of magnetic materials, such material isoften formed in the shape of a ring or toroid. These ring samples arethen wound with a layer of insulating tape and two or more windings ofwire are put over the tape. When many different material. compositionsare formed into rings of uniform size, each must have electricalwindings applied and removed for evaluation and tests. This process istedious and timeconsuming even if accomplished with the aid of a toroidwinding machine. Furthermore, a toroid winding machine does not alwaysaccommodate the large difference in wire diameter that would beconvenient to use for magnetic measurements.

Objects of the invention are to provide methods and structures toexpedite the determination of the magnetic characteristics of testsamples of materials to be evaluated.

More specifically, objects of the invention are to provide, in anelectrical system testing methods and structures facilitatingapplication of a pair of pre-formed current conductors to each of aseries of test samples in succession, in a manner to permit rapidtransfer from one to another of the series.

These and other advantages, features and objects of the invention willbecome more apparent from the following description taken in connectionwith the illustrative embodiments in the accompanying drawings, wherein:

Fig. 1 shows separately the toroidal sample and concentric insulators;

Fig. 2 shows the first stage of assembly with partial application of thedetector winding;

Fig. 3 shows a plan view in cross section of the sample afterapplication of the detector winding and insulators;

Fig. 4 shows the second stage of assembly with partial application ofthe primary winding;

Fig. 5 is the thumb screw clamping bar used in mounting the coils; and

Fig. 6 shows the device completely mounted and in operative form.

As will be clear from the drawings, the magnetic core sample 1 issurrounded by two insulator rings 2 and 3 which fit the inside andoutside peripheries of the core sample 1 snugly. The insulator rings 2and 3 may be made of Teflon about 0.05" thick which was chosen inlaboratory tests as the material for the insulating rings to support thewinding springs 4 and 7 because of low coefficient of friction togetherwith its mechanical strength and its excellent electricalcharacteristics. The anti- 2 friction characteristic of this materialallows easy threadingof close fitting windings of fine wire and manyturns. An alternative method would be the use of Teflon-covered springwire which would have the advantage of permitting the turns to be incontact allowing more turns to be used and eliminating the first twoinsulating rings 2 and 3. 7 a

The windings are made of a substance such as preformed Phosphor bronzesprings which are threaded over the Teflon insulators inclosing the coresamples. Inlaboratory tests the secondary or detector winding 4 was a 50turn winding made of 0.020" spring wire wound on a red with 54 turns totheinch. The primary winding 7 was made of 0.050" spring wire wound on a/2" rod with a spacing. equal to the diameter of the wire. These springwindings 4 and 7 have low electrical resistance, are non-magnetic andwithstand large distortions with nopermanent change in shape. They canbe thread-- ed on and off the core, samples many times without loss ofshape. The spring diameter can be determined by trial based on thematerial used. Too small a diameter makes threading difficult and causespermanent distortion in the spring; too large a diameter makes a bulkyassembly and decreases the spacing of the winding from the core sample.This excess spacing is not desirable, particularly in the winding whichsupplies the measuring instrument because of the possibility of errordue to stray fields. This consideration is not so important for theouter winding to which power is supplied.

In this type assembly, shorted turns are a possibility. However, such acondition is easily detected by holding the coil assembly in front of astrong light where the position of each turn may be readily observed.Correcting such a fault may be simply accomplished by moving the entirecoil or the offending turn slightly on the Teflon support rings andallowing the spring winding to assume its natural shape. After theapplication of the insulators 2, 3, 5 and 6 and the windings 4 and 7,the assembly is mounted on the Bakelite base 8 and held in place by athumb screw and plastic clamping bar 9. Connections are then made totapered pins 10 extending through the base mounting. The ends of theinner coil 4 may be formed into two turn loops of small diameter to holdtightly when pushed over the connected tapered pins 10. The heavy outercoil 7 can be formed in like manner. However, there is generallysuflicient spring tension stored in the outer coil winding 7 to make afirm contact by means of hooks shaped on the winding ends. The entireassembly can be accomplished without tools in less than four minutes.

Although the invention has been described with reference to particularembodiments it will be understood to those skilled in the art that theinvention is capable of a variety of alternative embodiments within thespirit and scope of the appended claims.

This application is a division of co-pending application No. 601,851,entitled Method and Means for Testing Magnetic Properties of ToroidCores, filed August 2, 1956, by Raymond A. MacMillan.

I claim:

1. The method of testing a series of toroidal magnetic cores of rigid,one-piece construction which comprises the steps of constraining a pairof electrical conductors into helical form, threading said pair ofhelical conductors around each of said cores in sequence, causing anelectric current to be supplied to one of said conductors, and observingthe magnitude of the current generated in the other of said conductors.

2. The method of testing a series of toroidal magnetic cores of rigid,one-piece construction which comprises the steps of constraining a pairof electrical conductors into helical form, placing the first helicalwinding thus formed Patented Jan. 24, 1961 about each of said cores insequence placing the second helical winding about said first winding,causing an electric current to be supplied to one of said windings, andobserving the magnitude of the current generated in the other of saidwindings.

3. A method for use in testing the magnetic properties of an annularbody which comprises the steps of forming a flexible electricalconductor into a helix whose turns are internally stressed to maintainthe helical form and threading said helical form onto said annular bodyto produce a current conducting toroid coil.

4. An electrical system comprising, in combination, a series of rigid,one-piece rings of insulating material of graduated sizes, said ringsbeing disposed in concentric re lationship and including inner and outerrings as well as a pair of medial rings, a magnetizable core disposedconcentrically between said pair of medial rings, a first prestressedconductor wound helically about the subassembly consisting of said coreand medial rings, a'

second pre'stressed conductor wound helically about the larger assemblyconsisting of said inner and outer rings and the conductor-enclosedsub-assembly disposed between said inner and outer rings, and means forsupplying 4 electric current to one of said conductors, to facilitateuse of the other conductor for indicating the degree of magnetization ofsaid core.

5. An electrical system comprising, in combination, a pair of rigid,one-piece rings of insulating material disposed in concentricrelationship, a magnetizable core disposed between said rings, a firstpre-stressed conductor wound helically about the sub-assembly consistingof said core and rings, a second pre-stressed conductor wound helicallyabout the larger assembly including said first pre-stressed conductor,said rings, and said core, and means including a second pair of rigid,one-piece rings for insulating said conductors, one from the other,

References Cited in the file of this patent UNITED STATES PATENTS1,320,980 Bowman Nov. 4, 1919 1,570,948 Crouch Jan. 26, 1926 1,695,679Berlowitz Dec. 18, 1928 1,897,604 Clemons Feb. 14, 1933 2,711,509 Endreset a1. June 21, 1955 2,829,338 Lord Apr. 1, 1958

